Add helper for verification of multiple properties

With the expectation that:
- we will add gpg checks;
- we may add a `verify` verb;
- we may introduce new means of verification, e.g. OS X's `codesign`

lib/hbc/verify.rb

@@ -1,6 +1,10 @@
 require 'digest'
 
 module Hbc::Verify
+  def self.all(path, cask)
+    checksum(path, cask)
+  end
+
   def self.checksum(path, cask)
     begin
       expected = cask.sha256